The present invention relates to cutting elements of the type which are mounted on rotary drill bits for cutting through formations, including rock formations, cement plugs, etc.
Rotary drilling operations in such formations are typically carried out using a rotary drill bit which is simultaneously rotated and advanced into the formation. Cutting is performed by cutting elements mounted on the drill bit, and the cuttings are flushed to the top of the borehole by the circulation of drilling fluid.
A conventional cutting element may comprise a cutting blank or abrasive compact mounted on a cemented carbide stud. The blank may include a thin diamond disk which is suitably secured to an inclined face of the stud, and the stud 18 is then secured, e.g., by press-fit, in a recess of the drill bit. Cutting elements of this type are disclosed, for example, in Rowley et al U.S. Pat. No. 4,073,354; Rohde et al U.S. Pat. No. 4,098,363; and Daniels et al U.S. Pat. No. 4,156,329.
The thin diamond disk of the cutting element is comprised of a cluster of abrasive diamond grains bonded together. Bonding of the abrasive cluster to the substrate can be effected either during or after the formation of the abrasive cluster. Attention is directed to U.S. Pat. Nos. 3,743,489, 3,745,623, and 3,767,761, for examples of various compacts and methods of fabricating same. One approach to such fabrication involves the placement of synthetic or natural diamond grains onto a circular flat surface of a cylindrical carbide substrate. The substrate is then placed in a press where the diamond grains and substrate are pressed together while being heated to a temperature below the degradation temperature of the diamond grains. If desired, a separate bonding medium can be mixed with the diamond grains. Pressure against the diamond grains is effected by a circular pressing surface of the same diameter as the substrate in order to achieve a uniform force distribution. There is thus formed an abrasive compact comprising a circular cylindrical substrate having a thin circular layer of bonded diamond grains thereon.
In certain types of cutting operations, it may be preferable to employ a cutting element which possesses a diamond layer of chisel-shape rather than circular shape. In those instances, it has been the practice to form an abrasive contact having a circular diamond layer, and thereafter grind away segments of the disc to a chisel shape. It will be appreciated that such an operation, especially the grinding of diamond, is difficult and costly. To attempt to otherwise fabricate the compact, for example, by configuring the substrate initially of chisel shape and placing that substrate, together with diamond grains, in a chisel-shaped press would not be practical because the presence of flats and corners along the side edges of the diamond layer would result in uneven radial pressures being imposed which would adversely affect the integrity of the bonding process.
It is, therefore, an object of the present invention to minimize or obviate problems of the type discussed above.
Another object is to provide a simpler and less costly method for fabricating chisel-shaped abrasive compacts.
A further object is to provide such a method which eliminates the need for appreciable grinding of diamond.